1. Field of the Invention
The present invention relates to a write-once data writing system for optical recording medium of a type wherein a data track includes a plurality of sectors each having at least a preamble and data.
2. Related Arts
In general, an optical recording medium has recording areas on which data is recorded as a pattern of changes in optical nature of the medium such as, reflectivity, transmissivity, polarization and the like. The patterns of changes are recorded by causing spots on the recording area to be physically or chemically transformed. Such changes are not reversible in most of optical recording media, which means that it is impossible to rewrite the data once written. However, there is a type of optical recording medium which allows additional data to be recorded only on areas not recorded yet. In recording data on such types of optical recording media, for example, a card type of optical recording medium, it is common to provide thereon information called "preamble" as sync regions operable in reading the recorded data.
The additional data recording may be performed a track-by-track or sector-by-sector manner.
In the former case wherein data is recordable on a track having no data recorded yet, the track is divided into a plurality of sectors each capable of storing a fixed or variable number of data with the preamble added at the beginning of each sector before recording data in the sector.
In the latter case wherein sectors of additional data are further recordable on the track which has several sectors of data previously recorded, the previously recorded sectors of data are read to detect the last recorded sector before recording additional data in the following sectors.
The track-by-track additional data recording system causes additional data to be recorded on a blank track separate from a recorded track even though the additional data is continued from the data on the recorded track. This results in a complex sequence of reading a series of data, increasing an access time.
Thus, this system does not satisfy the requirement that additional data is desirably recorded at an area following the area, on the same track, at which data is previously recorded.
Also, this system requires a number of blank tracks for recording additional data while leaving a lot of areas unused on a recorded track, degrading cost-performance and availability of recording area.
On the other hand, the sector-by-sector additional data recording system permits a series of data to be recorded continuously and in a sector-by-sector manner on the same track, which decreases unused area on each track, increasing availability of the recording area.
However, this system suffers from a serious disadvantage in its practical use by the following reasons:
In recording additional data on a track of the above-mentioned type of optical recording medium, the previously recorded data on the track is first read out to find the end in a reading mode and then the additional data is written in a writing mode. Generally, the data writing is quite different from the data reading in their operation speed due to difference in their function. That is, it takes a certain time in the writing mode to cause a phisical or chemical transomation with a light beam like a laser beam directed at a position on the optical recording medium while in the reading mode the operation is done almost instantaneously to detect, using a light beam, the change in optical state due to the previously formed phisical or chemical transformation. Therefore, the moving rate of the light beam for data writing is different from that for data reading. This results in complex control not only in timing for switching the mode from reading to writing but in setting of start position for writing.
One approach to overcome the problem is to read at the same rate as that is the writing mode. This yields another disadvantage that it takes much time to access a position at which additional data writing is started.
The present invention has been made to obviate the problems as described above and it is an object of the present invention to provide a write-one data writing system for optical recording medium which enables us to write a series of data continuously on the same track.
It is another object of the present invention to provide a write-once data writing system for optical recording medium which utilizes recording area efficiently with less unused region on each track.
It is yet another object of the present invention to provide a write-once data writing system for optical recording medium which is simple in control of switching a mode from reading to writing as well as in control of setting a start position for writing.
It is further object of the present invention to provide a write-once data writing system for an optical recording medium which realizes a practical system for recording additional data in a sector-by-sector manner.